Citing portfolio reassessment, two drug companies are returning pharmaceutical development rights to biotech partners. Merck & Co. has returned Parkinson’s drug candidates to Addex Pharmaceuticals, the Swiss firm that discovered them. Addex says it will continue to develop the drugs, known as allosteric modulators. Genzyme, meanwhile, has returned non-U.S. rights for ataluren, a treatment for muscular dystrophy and cystic fibrosis, to PTC Therapeutics. PTC already had U.S. rights to the drug, which is in clinical trials.